I am looking for suggestions about a small and compact CNC milling machine to sculpt decorative figures in metal and stone plates. I have no experience with such machines (I once saw an industrial one using high pressure water to cut through marble, but it's beyond my needs, budget and expertise), but I would not need a professional level machine, just a hobby level one with basic functionalities

micRo - ~$2000 (Need to buy a few pieces). This thing looks really nice, but has a small work area. The guy that makes them is fanatical about quality hobby equipment. http://lumenlab.com

DIY - ~$750. If you want to take the DIY approach and have a larger work area, pick up a copy of Build Your Own CNC Machine. The companion website literally has videos of the guy making the machine on a kitchen table with hand tools. I'm half way through the book and it appears surprisingly straight forward.